Furan fatty acids (F-acids) are a large group of fatty acids characterized by a furan ring, which carry at one α-position an unbranched fatty acid chain with 9, 11, or 13 carbon atoms and at the other α-position a short straight-chain alkyl group with 3 or 5 carbon atoms. Mostly two β-positions of the furan ring are substituted by either one or two methyl residues or another group. F-acids without any substitutions on both β-positions of the furan ring were also found in the seed oil of Exocarpus cupressiformis. F-acids are widely distributed in nature as trace components of plants, fishes, amphibians, reptiles, microorganisms and mammals including human.
Although the biological role of F-acids in the biological system is not fully understood, it has been pointed out that F-acids can be involved in various important biological functions acting as antioxidant, antitumoral and antithrombotic. In some fishes, F-acids include up to 25% of the acids in the liver lipids and accumulate during the spawning season, indicating a possible correlation between F-acids and the fertilization process. The correlation between consumption of fish rich in F-acid and protection against coronary heart disease mortality has been confirmed in several studies [(Spiteller, 2005, Lipids 40(8): 755-771), (Ishii et al., 1989, Chem Pharm Bull 37(5):1396-1398), (Graff et al., 1984, Biochim Biophys Acta 799(2):143-150), (Parker et al., 1977, J Med Chem 20(6):781-791)]. F-acid has also been reported to have inhibitory effects on blood platelets aggregation and to have potential antitumor activity. F-acids were found to prevent oxidation of linoleic acid and act as antioxidants in plants. Some studies demonstrated that F-acids underwent oxidation by ring opening to form dioxoenes in the presence of linoleic acid as co-substrate, demonstrating that F-acid acted as a radical scavenger.
Biosynthesis of F-acids is complicated and different. The biogenetic precursor of the most F-acids is known to be linoleic acid. It was recognized that plants synthesized the basic skeleton of F-acids. However, study with the radio-labeled feeding to fish indicated that fish synthesized neither the alkyl side chain nor the furan ring of F-acids. Therefore, F-acids in fish were considered to be originated from diet, especially algae. Consequently, F-acids are introduced into the human body through the diet like vegetables and fish. Diet-derived F-acids are incorporated into the tissue and blood of mammals, especially into phospholipids where they might act as radical scavengers resulting into inhibition of blood platelet aggregation.
As described above, various physiological activities of F-acids are well known. However, antimicrobial activity and antimicrobial effect against antibiotic combination treatment have not yet been confirmed.